Preeclampsia is a serious complication of pregnancy, affecting both the mother and fetus and causing an estimated 14% of pregnancy-related maternal deaths worldwide. Despite its large public health impact, however, its causes are still poorly understood, and there are no known treatments that effectively alleviate the risks for both mother and fetus. Based on clinical studies in humans and experimental studies in rodents, it has been suggested that the abnormal elevation of the circulating levels of soluble fms-like tyrosine kinase 1 (sFlt- 1) contributes to the systemic endothelial dysfunction and clinical manifestations of the disease through its antagonism of vascular endothelial growth factor (VEGF) activity. As a result, it is believed that VEGF treatment may reverse the preeclamptic phenotype caused by high sFlt-1 levels in the maternal circulation. However, in preliminary studies, we found, surprisingly, that overexpression of VEGF in pregnant mice results in elevated blood pressure, increased serum levels of sFlt-1 and soluble endoglin (sEng), and histological changes in the kidneys, similar to the clinical findings of PE in humans and animal models. VEGF has been shown to stimulate sFlt-1 production in several cell types and placental explant cultures in multiple contexts. However, the roles of placental VEGF at different stages of pregnancy, the significance of regulation of its local activity by placental production of sFlt-1, and its potential role in regulating sFlt-1 production in the placenta have never been examined, primarily due to lack of suitable animal models to test the placenta-specific effects of VEGF. We hypothesize that VEGF activity in the placenta is regulated in a placental developmental stage- specific manner during pregnancy through local production of sFlt-1, and placental VEGF levels may be a primary stimulus for increased production of sFlt-1 in this tissue. Studies in this proposal are designed, first, to develop a novel, inducible, placenta-specific gene expression system, with the ability to monitor gene expression throughout pregancy by live in vivo imaging. This technique will be based on established methods for viral delivery of genes specifically to placental tissue, effective control of consistency in gene expression levels, and a tightly controlled inducible promoter which allows expression to be rapidly switched both on and off. We will then examine the effects of different levels of placental VEGF expression at various time points during pregnancy using this inducible system. To define the physiological role of sFlt-1 during different stages of pregnancy, we will selectively knock down sFlt-1 expression in the placenta using placenta-specific expression of a short hairpin RNA (shRNA) targeted against sFlt-1. The results of these experiments will delineate, for the first time, the local interactions of VEGF and sFlt-1 in regulating VEGF activity in the placenta. Additionally, this entirely novel approach, using a newly-developed, inducible, placenta-specific gene regulation system, will greatly facilitate development of new animal models for the study of both placental disease and normal placental development and will greatly enable the development of therapies for complications of pregnancy.